Exhaust aftertreatment system

ABSTRACT

An exhaust aftertreatment system including an exhaust flow area, a first bank of one or more exhaust treatment devices in fluid communication with the exhaust flow area and a second bank of one or more exhaust treatment devices in fluid communication with the exhaust flow area. The first bank may be arranged in parallel with the second bank and inlet of the first bank is configured to provide greater flow resistance to the exhaust than the inlet of the second bank.

RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromU.S. Provisional Application No. 61/289,434 by Yung T. Bui et al., filedDec. 23, 2009, the contents of which are expressly incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to exhaust aftertreatment systems forremoving or reducing undesirable emissions from the exhaust of fossilfuel powered systems.

BACKGROUND

Exhaust aftertreatment systems are used to remove undesirable emissionsfrom the exhaust of fossil fuel powered systems (e.g. diesel engine, gasengines, gas turbines), which may be used to drive, for example,generators, commercial vehicles, machines, ships, and locomotives.Exhaust aftertreatment systems may include a variety of emissionstreatment technology, such as diesel oxidation catalysts (DOCs), dieselparticulate filters (DPFs), selective catalytic reduction catalysts(SCRs), lean NOx traps (LNTs) or other devices used to treat theexhaust.

Selective Catalytic Reduction (SCR) systems provide a method forremoving nitrogen oxide (NOx) emissions from fossil fuel poweredsystems. During SCR, a catalyst facilitates a reaction between areductant, such as ammonia, and NOx to produce water and nitrogen gas,thereby removing NOx from the exhaust gas. Generally, the reductant ismixed with the exhaust upstream of the SCR catalyst.

SCR may be more effective when a ratio of NO to NO₂ in the exhaustsupplied to the SCR catalyst is about 50:50. Some engines, however, mayproduce a flow of exhaust having a NO to NO₂ ratio of approximately95:5. In order to increase the relative amount of NO₂ to achieve a NO toNO₂ ratio of closer 50:50, a diesel oxidation catalyst (DOC) may belocated upstream of the SCR catalyst to convert NO to NO₂. DOCs are alsoused to remove carbon monoxide and hydrocarbons from the exhaust.

Exhaust aftertreatment systems may be installed as original equipment ormay be retrofitted to a specific application. To facilitate easierinstallation, some exhaust aftertreatment systems are preassembled withcomponents enclosed within a common housing. U.S. Published PatentApplication No. 2008/0314033, by Aneja et al. (hereinafter the '033application), discloses such a system. The '748 application discloses agenerally cubical common housing that encloses a pair of DOC/DPFs, areducing agent injector, a mixing chamber, and a pair of SCR catalysts.Exhaust entering the system is split into two flow streams that aredirected through the two DOC/DPFs in parallel. The exhaust is recombinedinto a single stream to which the reducing agent is injected and issplit again into two streams that flow through the two SCR catalysts inparallel.

While the system disclosed in the '033 application may be suitable toreduce target emissions in some applications, specific size andbackpressure constraints, specific emissions requirements and otherrequirements may make it unsuitable for other applications.

SUMMARY

In one aspect, the present disclosure provides an aftertreatment systemfor treating exhaust from an engine. The system including an exhaustflow area, a first bank of one or more exhaust treatment devices influid communication with the exhaust flow area and a second bank of oneor more exhaust treatment devices in fluid communication with theexhaust flow area. The first bank may be arranged in parallel with thesecond bank and inlet of the first bank is configured to provide greaterflow resistance to the exhaust than the inlet of the second bank

In another aspect, the present disclosure provides a method for treatingthe exhaust of an engine. The method includes directing the exhauststream into an exhaust flow region in fluid communication with a firstbank of one or more exhaust treatment device and in fluid communicationa second bank of one or more exhaust treatment devices and resisting theflow of exhaust into the first bank of one or more exhaust treatmentdevices more than resisting the flow of exhaust into the a second bankof one or more exhaust treatment devices.

Other features and aspects of this disclosure will be apparent from thefollowing description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which are incorporated in and constitute apart of this specification, exemplary embodiments of the disclosure areillustrated, which, together with the written description, serve toexplain the principles of the disclosed system:

FIG. 1 is a schematic view of a first embodiment of a power systemaccording to the present disclosure;

FIG. 2 is a perspective view of second embodiment of a power systemaccording to the present disclosure;

FIG. 3 is a top cross-sectional view of an embodiment of an exhaustaftertreatment system of the power system of FIG. 2;

FIG. 4 is a perspective cross-sectional view the exhaust aftertreatmentsystem of FIG. 3;

FIG. 5 is a partial sectioned perspective view of an inlet portion ofthe exhaust aftertreatment system of FIG. 3;

FIG. 6 is a partial sectioned end view of the inlet portion of FIG. 5;and

FIG. 7 is a perspective view of the intermediate flow region of theexhaust aftertreatment system of FIG. 3.

DETAILED DESCRIPTION

Referring to FIG. 1, an embodiment of a power system 10 is disclosed.The power system 10 includes an engine 12 and an exhaust aftertreatmentsystem 14 configured to treat one or more exhaust stream(s) 16 producedby the engine 12. The engine 12 may include features not shown, such asfuel systems, air systems, cooling systems, peripheries, drivetraincomponents, turbochargers, etc. The engine 12 may be any type of engine(internal combustion, turbine, gas, diesel, gaseous fuel, natural gas,propane, etc.), may be of any size, with any number of cylinders, and inany configuration (“V,” in-line, radial, etc.). The engine 12 may beused to power any machine or other device, including locomotiveapplications, on-highway trucks or vehicles, off-highway trucks ormachines, earth moving equipment, generators, aerospace applications,marine applications, pumps, stationary equipment, or other enginepowered applications.

The exhaust aftertreatment system 14 includes a housing 18 configured toentirely or partially enclose one or more exhaust aftertreatment devicesdesigned to reduce undesirable emissions from the exhaust stream(s) 16of the engine 12. The exhaust aftertreatment devices may include avariety of emissions treatment technology, including, but not limitedto, regeneration devices, heat sources, oxidation catalysts, dieseloxidation catalysts (DOCs), diesel particulate filters (DPFs), selectivecatalytic reduction catalysts (SCRs), lean NOx traps (LNTs), mufflers,or other devices needed to treat the exhaust stream 16 exiting theengine 12.

In the depicted embodiment, the exhaust aftertreatment system 14includes one or more first aftertreatment device(s) 20 and one or moresecond aftertreatment device(s) 22. In one embodiment, the one or morefirst aftertreatment device(s) 20 are one or more DOC(s) and the one ormore second aftertreatment device(s) are one or more SCR catalyst(s). Inthe depicted embodiment, the exhaust stream 16 enters the housing 18 atone or more exhaust inlet(s) 24, passes through the one or more firstaftertreatment device(s) 20 (in series or in parallel), then passesthrough the one or more second aftertreatment device (s) 22 (in seriesor in parallel), and exits the housing 18 via one or more exhaustoutlet(s) 26.

The exhaust aftertreatment system 14 also includes a reductant supplysystem 28 and an intermediate flow region 30. The reductant supplysystem 28 is configured to introduce a reductant into the exhauststream(s) 16. The reductant supply system 28 may be configured in avariety of ways. Any system capable of supplying a desired amount ofreductant on-demand to the exhaust stream 16 may be used. For example,the reductant supply system 28 includes a reductant source 32, a pump34, a valve 36, and an injector 38 in fluid communication with thereductant source 32. The reductant source 32 may be a tank, vessel,absorbing material, or other device capable of storing and releasing thereductant. The reductant may be urea, ammonia, diesel fuel, or someother hydrocarbon used by the one or more second aftertreatmentdevice(s) 22 to reduce or otherwise remove NOx or NO emissions from theexhaust stream 16. If the reductant used in the system is the same asthe fuel used to power the engine 12, then the reductant source 32 maybe a fuel tank of power system 10.

The pump 34 may be any an extraction device capable of pulling reductantfrom the reductant source 32. The valve 36 is included to help regulateor control the delivery of reductant. The injector 38 may be any devicecapable of introducing reductant in the exhaust stream 16.

The intermediate flow region 30 is configured to mix the reductant withthe exhaust stream 16 prior to introducing the mixture into the one ormore second aftertreatment device(s) 22. The intermediate flow region 30may include structures that enhance disruption of the flow stream and/orprovide adequate time for the exhaust and reductant to sufficiently mix.

The power system 10 may also include one or more controllers 40configured to control and monitor the operation of the engine 12 and theexhaust aftertreatment system 14. The power system 10 may have a singlecontroller that controls and monitors both the engine 12 and the exhaustaftertreatment system 14, or multiple controllers that control andmonitor various portions of the power system 10. For example, the powersystem 10 may have a first controller that is in communication with theengine 12 to control and monitor the operation of the engine and mayhave a second controller that is in communication with the reductantsupply system 28 to control the pump 34 and valve 36 and monitor thevarious aspects of the reductant supply system, such as for example, theamount of reductant available from the reductant source 32. The firstand second controllers may also be in communication with each other.

The one or more controllers 40 may be in communication with varioussensors associated with the exhaust aftertreatment system 14 to receivesignals from the sensors indicative of characteristics of the exhaustand/or exhaust aftertreatment system 14. The sensors may be positionedat any suitable location within the exhaust aftertreatment system 14 tomonitor desired characteristics of the exhaust and/or exhaustaftertreatment system. In the depicted embodiment, one or more pressuresensors 42 are associated with the one or more first aftertreatmentdevice(s) 20 to monitor the change in exhaust pressure across thedevice(s). In addition, a NOx sensor 44 is positioned downstream of theone or more first aftertreatment device(s) 20 to provide a signalindicative of the NOx content of the exhaust. Furthermore, one or moresensors 46 may be associated with the one or more second aftertreatmentdevice(s) 20 to provide signals indicative of the temperature of theexhaust entering or exiting the one or more second aftertreatmentdevice(s) and the NOx content of the exhaust exiting the one or moresecond aftertreatment device(s).

Referring to FIG. 2, a second embodiment of a power system 210 isdisclosed. The depicted power system 210 is embodied as a locomotivehaving an engine 212, a fuel tank 213, and an exhaust aftertreatmentsystem 214. The engine 212 is at least partially enclosed within a body215 of the locomotive and the exhaust aftertreatment system 214 isexternally mounted on the top of the body 215 (such as on a roof 211 ofthe locomotive body). In other embodiments, however, the exhaustaftertreatment system 214 may be at least partially mounted within thebody 215. One or more exhaust conduit(s) 216 connect the engine 212 tothe exhaust aftertreatment system 214 to route one or more exhauststream(s) 217 (see FIGS. 3 and 5) from the engine 212 to the exhaustaftertreatment system 214.

The exhaust aftertreatment system 214 includes various emissionstreatment devices to reduce undesirable emissions from the exhauststream(s) 217 of the engine 212. The emissions treatment devices mayinclude a variety of emissions treatment technology, including, but notlimited to, regeneration devices, heat sources, oxidation catalysts,diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs),selective catalytic reduction catalysts (SCRs), lean NOx traps (LNTs),mufflers, or other devices capable of treating the exhaust from a powersystem. The exhaust aftertreatment system 214 includes a housing 218that entirely or at least partially encloses the emissions treatmentdevices. The housing 218 includes a top wall 220, a bottom wall 222, andone or more side walls 224.

The exhaust aftertreatment system 214 also includes a reductant supplysystem 226. The reductant supply system 226 includes a dosing assembly228 and a reductant source 229 in fluid communication with the dosingassembly 228. The dosing assembly 228 may include various components(not shown) (e.g. such as pumps, valves, injectors, etc.) operable tosupply a desired amount of reductant to the system on-demand.

Referring to FIGS. 3 and 4, an embodiment of the exhaust aftertreatmentsystem 214 is disclosed. The exhaust aftertreatment system 214 may beconfigured in a variety of shapes and sizes depending on theapplication. In the depicted embodiment, the exhaust aftertreatmentsystem 214 is a generally rectangular box-shaped structure having aheight dimension H (FIG. 4), a length dimension L (FIG. 3), and a widthdimension W (FIG. 3). In one embodiment, the height H is less than about94.5 cm, the length L is less than about 258 cm, and the width W is lessthan about 226 cm. Thus, the total volume of the system is less thanabout 5.5101 cubic meters. In another embodiment, the height H isapproximately 89.5 cm, the length L is approximately 253 cm, and thewidth W is approximately 221 cm. Thus, the total volume of the system isabout 5.0042 cubic meters.

Referring to FIG. 5, the exhaust aftertreatment system 214 includes afirst exhaust inlet 230 configured to receive a first entering exhaustflow 217 a and a second exhaust inlet 232 configured to receive a secondentering exhaust flow 217 b disposed through the bottom wall 222. Afirst conduit 233 fluidly couples the first exhaust inlet 230 to a firstDOC housing 234. The first DOC housing 234 forms a chamber 236. A firstdiffuser 237 is coupled to the first conduit 233 and is disposed withinthe chamber 236.

Referring to FIG. 6, the first diffuser 237 may be configured in avariety of ways. Any structure capable of reducing the swirl of theexhaust entering the first DOC housing and spreading out the flow of thefirst entering exhaust stream 217 a may be used. In the depictedembodiment, the first diffuser 237 is hollow with a generally circular,oval, elliptical, or rectangular cross-section. The first diffuser 237has a first end 238 coupled to the first conduit 233 and a distal secondend 239. The first diffuser 237 includes a plurality of apertures orperforations 240 configured to allow the exhaust to flow from theinterior of the first diffuser 237 into the chamber 236. The firstdiffuser 237 may be configured to provide an increasing resistance toflow along the length of the first diffuser 237 toward the distal secondend 239. For example, in the depicted embodiment, the first diffuser 237tapers inward such that the cross-section of the hollow interiordecreases in size along its length toward the distal second end 239. Inother embodiments, however, the first diffuser 237 may not be tapered.

The plurality of openings or perforations 240 may also be configured toprovide an increasing resistance to flow exiting the first diffuser 237along the length toward the distal second end 239. For example, theplurality of openings or perforations 240 may decrease in number and/oreach of the plurality of apertures or perforations 240 may decrease insize along the length of the first diffuser 237.

A first baffle 241 is positioned in the first exhaust inlet 232 toassist in directing the first entering exhaust stream 217 a into thefirst diffuser 237. The first baffle 241 is configured to split thefirst exhaust inlet 232 into two sections. In the depicted embodiment,the first exhaust inlet 232 is curved and the first baffle 241 ispositioned within the curve to promote an even flow distribution ofexhaust entering the first diffuser 237.

The configuration of the first diffuser 237 and the first baffle 241help provide an exhaust flow within the first DOC housing 234 with aneven distribution and low swirl.

One or more DOC(s) are also disposed within the first DOC housing 234.The DOC(s) may be configured in a variety of ways and contain catalystmaterials useful in collecting, absorbing, adsorbing, and/or convertinghydrocarbons, carbon monoxide, and/or oxides of nitrogen contained inthe exhaust. Such catalyst materials may include, for example, aluminum,platinum, palladium, rhodium, barium, cerium, and/or alkali metals,alkaline-earth metals, rare-earth metals, or combinations thereof. TheDOC(s) may include, for example, a ceramic substrate, a metallic mesh,foam, or any other porous material known in the art, and the catalystmaterials may be located on, for example, a substrate of the DOC(s). TheDOC(s) assist in oxidizing one or more components of the exhaust flow,such as, for example, particulate matter, hydrocarbons, and/or carbonmonoxide. The DOC(s) are also configured to oxidize NO contained in theexhaust gas, thereby converting it to NO2. Thus, the DOC(s) assist inachieving a desired ratio of NO to NO2 upstream of the SCR(s).

In the depicted embodiment, a first DOC 242 a and a second DOC 242 b aredisposed within the first DOC housing 234 in series. The first andsecond DOCs 242 a, 242 b are generally cylindrical substrates with adiameter D_(D) (FIG. 4) greater than about 58 cm and a thickness T_(D)greater than about 7 cm. Thus, the volume of the each DOC is greaterthan about 18494.56 cubic centimeters. In another embodiment, thediameter D_(D) is greater than about 60.9 cm and the thickness T_(D)greater than about 8.9 cm. Thus, the volume of the each DOC is greaterthan about 25924.74 cubic centimeters. The characteristics of the firstDOC 242 a (i.e. shape, size, the type of catalyst coating, the number ofcells per squire inch, etc.) may be similar to the second DOC 242 b ormay be different.

The first DOC housing 234 includes a first DOC support structure 244.The first DOC support structure 244 may be configured in a variety ofways. Any structure capable of supporting the DOC(s) 242 a, 244 b in adesired orientation and providing a seal such that exhaust directedthrough the catalysts does not leak or escape around the edges of thecatalysts may be used.

Adjacent a first DOC housing outlet 246 is a first redirecting flowpassage 248. The first redirecting flow passage 248 is configured toredirect the flow of the first entering exhaust stream 217 a from thefirst DOC housing outlet 246 to an inlet 250 of an intermediate flowregion 251 (described in detail below). One or more walls or baffles 252are utilized to aid in redirecting the flow of exhaust.

The structure and components described above from the first exhaustinlet 230 to the first redirecting flow passage 248 are similar to thestructure and components from the second exhaust inlet 232 to a secondredirecting flow passage 254, including a second conduit 256, a seconddiffuser 258, a second DOC housing 260, a third and fourth DOCs 262 a,262 b, and a second DOC support structure 264.

The first redirecting flow passage 248 and the second redirecting flowpassage 254 merge the exhaust from the first exhaust inlet 230 and thesecond exhaust inlet 234 at the intermediate flow region inlet 250.Positioned in the proximity of the intermediate flow region inlet 250 isa reductant inlet 266 (see FIG. 3). As discussed above regarding FIG. 2,the power system 210 includes a reductant supply system 226. Thereductant supply system 226 is configured to introduce reductant, suchas urea for example, into the exhaust stream 217 at the reductant inlet266. The reductant inlet 266 may be, for example, an injector or otherdispensing device adapted to introduce the reductant into the exhaust.

The intermediate flow region 251 may be configured in a variety of ways.For example, the intermediate flow region 251 may be configured to allowsufficient mixing of the exhaust and the reductant prior to the mixtureentering into a downstream emission control device. In the depictedembodiment, the intermediate flow region 251 includes a mixing tube 270and a diffuser or mixing device 272. The mixing tube 270 is a generallycylindrical tube extending along a longitudinal axis 273. The mixingtube 270 has an open end defining the intermediate flow region inlet 250and a closed end 274 distal from the intermediate flow region inlet 250.Adjacent the closed end 274 are a plurality of radially spaced openings276 around at least a portion of the circumference of the mixing tube270. Thus, the plurality of radially spaced openings 276 may bepositioned around the entire circumference of the mixing tube 270 oraround a portion of the circumference, such as for example, around thecircumference except at approximately the 90 degrees position and the270 degree position where the zero degree position is at top verticalposition as oriented in FIGS. 4 and 7. The openings 276 define the exitof the mixing tube 270 and may be configured in a variety of ways (e.g.shape, size, location along the circumference of the mixing tube).

Referring to FIG. 7, the mixing tube 270 has a total length Lt (distancefrom the intermediate flow region inlet 250 to the closed end 274) thatis about 75% or greater than the exhaust aftertreatment system length L.The mixing tube 270 may have a length to openings Lo (distance from theintermediate flow region inlet 250 to the first of the plurality ofradially spaced openings 276) that is about 55% or greater than theexhaust aftertreatment system length L. In one embodiment, the totallength Lt is about 80% or greater the system length L and the length toopenings Lo is about 60% or greater than the system length L.

In one embodiment, the total mixing tube length Lt is greater than about200 cm and the length to opening Lo is greater than about 149 cm. Inanother embodiment, the mixing tube total length Lt is about 202.5 cmand the mixing tube length to opening Lo is about 151.5 cm.

Referring to FIGS. 3-4, the diffuser or mixing device 272 may be anystructure capable of disrupting the flow of the exhaust stream 217 andfacilitating dispersion of reductant into the exhaust stream 217. Thediffuser or mixing device 272 may include orifices, deflectors,swirlers, baffles, or other structures that disrupt flow of the exhauststream 217. The diffuser or mixing device 272 may be positioned withinthe mixing tube 270 and held in place by any suitable means. Thediffuser or mixing device 272 may be positioned along the mixing tubelength Lt at any suitable location. In the depicted embodiment, thediffuser or mixing device 272 is positioned closer to the intermediateflow region inlet 250 than to the closed end 274.

Positioned radially outward of the mixing tube openings 276 is an SCRinlet exhaust flow region 278. In fluid communication with the SCR inletexhaust flow region 278, and on opposites sides of the mixing tube 270,are a first SCR assembly 280 and a second SCR assembly 282. The SCRinlet exhaust flow region 278 may be common to both the first SCRassembly 280 and a second SCR assembly 282 or may be divided intoseparate flow areas associated with each of the SCR assemblies. Thefirst SCR assembly 280 is similar in structure and function to thesecond SCR assembly 282, thus only the first SCR assembly 280 will bedescribed in detail.

The first SCR assembly 280 includes a first SCR bank 284 that includesat least a first SCR catalyst(s) 286, a second SCR bank 288 thatincludes at least a second SCR catalyst(s) 290, and a SCR supportstructure 292 configured to support the SCR catalysts in a desiredorientation. The SCR catalyst(s) 286, 290 may be configured in a varietyof ways. The SCR catalyst(s) 286, 290 may be any suitable SCR catalyst,such as for example, a vanadium and titanium-type, a platinum-type, or azeolite-type SCR catalyst, and includes a metallic or ceramic honeycombsubstrate or other structure containing one or more of these metals andconfigured to assist in reducing NOx. The SCR catalyst(s) 286, 290 mayhave an optimum or peak NOx conversion rate when the ratio of NO to NO2entering the SCR catalyst(s) 286, 290 is approximately one to one.

In the depicted embodiment, the first SCR bank 284 includes a first SCRbank inlet 294, four SCR catalysts 286 oriented in series, and a firstSCR bank outlet 296. The second SCR bank 288 includes a second SCR bankinlet 298, four SCR catalysts 290 arranged in series, and a second SCRbank outlet 300. The second SCR bank 288 is arranged in parallel withthe first SCR bank 284.

The SCR catalysts 286, 290 in the depicted embodiment have generallyrectangular substrate (or rectangular with rounded corners) with aheight H_(S) and width W_(S) greater than about 59 cm and a thicknessT_(S) greater than about 7 cm. Thus, each catalyst substrate has avolume greater than about 24367 cubic centimeters. In anotherembodiment, the SCR catalysts 286, 290 have a height H_(S) and widthW_(S) greater than about 60.9 cm and a thickness T_(S) greater thanabout 8.9 cm. Thus, each catalyst substrate has a volume greater thanabout 33008.4 cubic centimeters. The characteristics of the each of theSCR catalyst (i.e. shape, size, the type of catalyst coating, the numberof cells per squire inch, etc.) may be similar to each other or may bedifferent.

The first SCR bank inlet 294 is positioned generally adjacent theradially-spaced openings 276 while the second SCR bank inlet 298 ispositioned axially closer to the intermediate flow region inlet 250. Thefirst SCR bank inlet 294 is configured to resist the flow of exhaustinto the first SCR bank 284 more than the second SCR bank inlet 298resists flow of exhaust into the second SCR bank 288. This may beaccomplished in a variety of ways. For example, the total orifice areaof the first inlet may be smaller than the total orifice area of thesecond inlet. Referring to FIG. 7, in the depicted embodiment, the firstSCR bank inlet 294 is defined by a first plurality of openings 302 andthe second SCR bank inlet 298 is defined by a second plurality ofopenings 304. Each of the second plurality of openings 304 is largerthan each of the first plurality of openings 302. As a result, the firstplurality of openings 302 resists flow more than the second plurality ofopenings 304.

Referring to FIGS. 3 and 4, the first SCR bank outlet 284 and the secondSCR bank outlet 288 open to a common first exhaust manifold 306 thatdefines a first exhaust exit passage. The first exhaust manifold 306 isconfigured to direct exhaust vertically upward where it exits the systemfrom or adjacent to the top wall 220.

As indicated above, the first SCR assembly 280 is similar in structureand function to the second SCR assembly 282. Thus, the second SCRassembly 282 includes a third SCR bank 310 having a third SCR bank inlet312, four SCR catalysts 314 oriented in series, and a third SCR bankoutlet 316. The second SCR assembly 282 further includes a fourth SCRbank 318 having a fourth SCR bank inlet 320, four SCR catalysts 322arranged in series, and a fourth SCR bank outlet 324. The third SCR bank310 is arranged in parallel with the fourth SCR bank 318. The third SCRbank outlet 316 and the fourth SCR bank outlet 324 open to a commonsecond exhaust manifold 330 that defines a second exhaust exit passage.

As evident from FIGS. 3 and 4, the exhaust aftertreatment system 214 maybe generally symmetric about the longitudinal axis 273, though that isnot required.

Industrial Applicability

The disclosed exhaust aftertreatment system 214 provides an efficient,compact, reliable way to reduce undesirable emissions released into theatmosphere. The disclosed exhaust treatment system may be used to reduceundesirable exhaust emissions from a power system 210 in a variety ofapplications, such as but not limited to, locomotive applications,on-highway trucks or vehicles, off-highway trucks or machines, earthmoving equipment, generators, aerospace applications, marineapplications, pumps, stationary equipment, or other engine poweredapplications. In particular, the disclosed exhaust aftertreatment system214 is well-suited for installation on a diesel locomotive.

In particular, referring to FIGS. 2-4, the exhaust aftertreatment system214 mounts onto the roof of the power system 210 such that the top wall220 and one or more of the side walls 224 are external to the body 215and exposed to atmosphere. In this mounting arrangement, the exhaustaftertreatment system 214 is isolated from the engine heat and exposedto atmosphere for improved heat rejection versus an internal mountedsystem.

Since first exhaust inlet 230 and the second exhaust inlet 232 aredisposed on the bottom wall 222, connection to the engine is convenientwith minimal length of the exhaust conduit 216 required. For conveniencein describing the exhaust flow, the power system 210 is assumed to be ona horizontal surface. Exhaust flow through the exhaust aftertreatmentsystem 214 is illustrated with arrows in FIG. 3.

The first and second entering exhaust streams 217 a, 217 b from theengine 212 enter the first exhaust inlet 230 and the second exhaustinlets 232, respectively, in a generally vertical direction. The firstand second conduits 233, 256, and the first and second DOC housings 234,260 are configured to redirect the entering exhaust streams 217 a, 217 babout 90 degrees into a horizontal flow direction and through the DOCs242, 262. Once through the DOCs 242, 262, the redirecting flow passages248, 254 turn the streams about 180 degrees and merge the two streams atthe intermediate flow region inlet 250 generally along the longitudinalaxis 273.

In the proximity of the mixing region inlet 250, the reductant supplysystem 226 introduces reductant into the merged exhaust stream 217,which flows down the mixing tube 270 and through the mixing device 272.The configuration of the exhaust aftertreatment system 214 provides amixing tube length Lt that is about 75% to 80% the length L to theentire exhaust aftertreatment system 214. When urea is used as areductant, a longer resonance time of the exhaust/reductant mixture inthe mixing tube 270 helps create a homogenized dispersion of reductantin the exhaust, which helps ensure sufficient decomposition of the ureainto ammonia (NH3).

Near the mixing tube closed end 274, the exhaust exits the mixing tube270 radially through the openings 276. Thus, the openings 276 and mixingtube 270 are configured to redirect the exhaust stream 217 about 90degrees from a generally axial flow direction to a generally radial flowdirection. By configuring the mixing tube 270 to redirect the exhaustflow from axial to radial, the mixing tube length Lt can be maximizedwithin the constraints of the housing. After exiting the mixing tube270, the exhaust steam 217 flows into the SCR inlet exhaust flow region278 and splits into a first exiting exhaust stream 217 c and a secondexiting exhaust stream 217 d that flow through the first SCR assembly280 and the second SCR assembly 282, respectively. The first exitingexhaust stream 217 c is further divided into a third exhaust stream anda fourth exhaust stream that flow through the first SCR bank 284 and thesecond SCR bank 288, respectively. Though the first SCR bank inlet 294and the third SCR bank inlet 312 are closer to the radial openings 276,exhaust flow through the SCR catalyst banks is balanced because thefirst SCR bank inlet 294 and the third SCR bank inlet 312 are configuredto provide greater flow resistance than the second SCR bank inlet 288and the fourth SCR bank inlet 320.

Since the exhaust stream 217 is redirected about 90 degrees from agenerally axial flow direction to a generally radial flow direction toflow through the SCR catalyst assemblies 280, 282 when mounted onto thepower system 210, the orientation of the SCR substrate face may begenerally perpendicular to the travel direction of the power system 210.This provides less dynamic impact force on the SCR substrates. Inaddition, the parallel arrangement to the SCR catalyst banks 284, 288,310, 318 help to minimize exhaust back pressure in the system.

Once through the SCR catalyst assemblies 280, 282, the exhaust manifolds306, 330 redirect the exhaust about 90 degrees to a vertical directionthat exits the exhaust aftertreatment system 214 from or adjacent to thetop wall 220.

Freight locomotives are intended for interchange service are subject tosize constraints. For example, the Association of American Railroad(AAR) Plate L diagram defines the clearance envelope for freightlocomotives intended for interchange service (see AAR manual ofStandards and Recommended Practices—Locomotives and LocomotiveInterchange Equipment). Thus, any locomotive exhaust aftertreatmentsystem, originally manufactured or retrofitted, must be positioned andsized to ensure that the locomotive remains within the requiredclearance envelope.

The disclosed exhaust aftertreatment system 214 may be sized such thatit can be mounted onto the roof of a locomotive without resulting in thelocomotive exceeding the AAR Plate L clearance envelope. Furthermore,the system, while roof-mounted, has the capability of reducing exhaustemissions below current anticipated EPA Tier 4 emissions regulations forNOx (i.e. 1.3 g/bhp-hr) while keeping exhaust backpressure below about8.5 kPa when the locomotive is running at rated power (i.e. notch 8). Inother embodiments, the exhaust backpressure is kept below about 7.9 kPawhen the locomotive is running at rated power (i.e. notch 8).

Thus, the disclosed exhaust aftertreatment system may include a totalDOC substrate volume greater than about 73,980 cubic centimeters, atotal SCR catalyst substrate volume greater than about 389,875 cubiccentimeters, a mixing tube total length of about 75% or greater than thetotal length of the exhaust aftertreatment system, enclosed in a housingwith a the height less than about 94.5 cm, a length L less than about258 cm, and a width W less than about 226 cm. The system beingconfigured to keep exhaust backpressure below about 8.5 kPa when thelocomotive is running at rated power (i.e. notch 8).

Although the embodiments of this disclosure as described herein may beincorporated without departing from the scope of the following claims,it will be apparent to those skilled in the art that variousmodifications and variations can be made. Other embodiments will beapparent to those skilled in the art from consideration of thespecification and practice of the disclosure. It is intended that thespecification and examples be considered as exemplary only, with a truescope being indicated by the following claims and their equivalents.

What is claimed is:
 1. An aftertreatment system for treating an exhaustfrom an engine, comprising: a first exhaust flow region; a first bank ofone or more exhaust treatment, the first bank having a first inlet influid communication with the first exhaust flow region; and a secondbank of one or more exhaust treatment devices having a second inlet influid communication with the exhaust flow region; the first bankarranged in parallel with the second bank; wherein the first inlet isconfigured to provide greater flow resistance to the exhaust than thesecond inlet; and a housing exclusive of the engine containing the firstexhaust flow region, the first bank of one or more exhaust treatmentdevices and the second bank of one or more exhaust treatment devices. 2.The exhaust treatment system of claim 1 wherein the first inlet has afirst group of openings and the second inlet has a second group ofopenings, wherein the first group of openings has a smaller total flowarea than the second group of openings.
 3. The exhaust treatment systemof claim 1 further comprising a second exhaust flow region in fluidcommunication with and upstream from the first exhaust flow region, thesecond exhaust flow region extending along a longitudinal axis, whereinthe system is configured to flow exhaust through the first bank of oneor more exhaust treatment devices in a direction substantiallyperpendicular to the longitudinal axis.
 4. The exhaust treatment systemof claim 3 wherein the second exhaust flow region is configured todirect exhaust into the first exhaust flow a region in a radialdirection.
 5. The exhaust treatment system of claim 3 wherein the secondexhaust flow region includes a flow passage having an open end definingan inlet, a closed end opposite the open end, and a plurality of radialopenings adjacent the closed end defining an outlet.
 6. The exhausttreatment system of claim 1 comprising an exhaust inlet passage upstreamof second exhaust flow region, the exhaust inlet passage being coupledto a diffuser having a plurality of apertures.
 7. The exhaust treatmentsystem of claim 6 comprising baffle within the exhaust inlet passageupstream of diffuser, the baffle being configured to divide the exhauststream entering the diffuser.
 8. The exhaust treatment system of claim 6wherein the plurality of apertures decrease in size toward a distal endof the diffuser.
 9. The exhaust treatment system of claim 6 wherein thediffuser tapers inward toward a distal end of the diffuser.
 10. Theexhaust treatment system of claim 6 wherein the diffuser is positionedupstream of a diesel oxidation catalyst.
 11. A power source, comprising:an engine; an exhaust conduit configured to receive exhaust from theengine; an exhaust treatment system in fluid communication with theexhaust conduit, the exhaust treatment system comprising: a firstexhaust flow region; a first bank of one or more exhaust treatmentdevices in fluid communication with the exhaust flow area, the firstbank having a first inlet configured to receive exhaust directly fromthe first exhaust flow region; a second bank of one or more exhausttreatment devices in fluid communication with the exhaust flow area; thefirst bank arranged in parallel with the second bank, the second bankhaving a second inlet configured to receive exhaust directly from thefirst exhaust flow region, wherein the first inlet is configured toprovide greater flow resistance to the exhaust than the second inlet;and a housing exclusive of the engine containing the first exhaust flowregion, the first bank of one or more exhaust treatment devices and thesecond bank of one or more exhaust treatment devices.
 12. The powersource of claim 11 wherein the first inlet has a first group of openingsand the second inlet has a second group of openings, wherein the firstgroup of openings has a smaller total flow area than the second group ofopenings.
 13. The power source of claim 11 comprising a second exhaustflow region in fluid communication with and upstream from the firstexhaust flow region, the second exhaust flow region extending along alongitudinal axis, wherein the system is configured to flow exhaustthrough the first bank of one or more exhaust treatment devices in adirection substantially perpendicular to the longitudinal axis.
 14. Theexhaust treatment system of claim 13 wherein the second exhaust flowregion includes a flow passage having an open end defining an inlet, aclosed end opposite the open end, and a plurality of radial openingsadjacent the closed end defining an outlet.
 15. The exhaust treatmentsystem of claim 13 comprising an exhaust inlet passage upstream ofsecond exhaust flow region, the exhaust inlet passage being coupled to adiffuser.
 16. The exhaust treatment system of claim 15 comprising bafflewithin the exhaust inlet passage upstream of diffuser, the baffle beingconfigured to divide the exhaust stream entering the diffuser.
 17. Theexhaust treatment system of claim 8 wherein the diffuser is hollow andincludes a plurality of apertures that decrease in size toward a distalend of the diffuser.